(USA TODAY) -- Isaac started losing strength earlier in the day with sustained winds of 75 mph, the National Hurricane Center reported. Late Wednesday afternoon, Isaac was located about 50 miles west southwest of New Orleans moving to the northwest at 6 mph.

In Vermilion Parish, a 36-year-old man fell to his death after climbing up a tree during the storm, though authorities don't know why he did this, Sheriff Mike Couvillon said.

About 8,200 guardsmen across the state were on hand to help with relief missions and other duties, including providing security in parishes, such as Orleans, Jefferson and Plaquemines, Gov. Bobby Jindal said.

"Our focus will be on lifesaving missions across these parishes," Jindal said.

At a news conference in Baton Rouge, the governor said officials may cut a hole in a levee on the east bank of Plaquemines Parish to relieve pressure on the structure.

The parish, about 50 miles southeast of New Orleans, was one of the worst hit areas. Water spilled over a levee there in a 12-foot storm surge late Tuesday that flooded homes and stranded some residents.

Isaac passed directly over the region of marshland, fishing towns and marinas, peeling off roofs and flooding some areas.

The northern part of the parish is ringed in by the area's hurricane protection system of fortified levees and floodwalls. Stretches of it on the east bank of the Mississippi River and farther south lie outside the protection system, making it vulnerable to storm surge and flooding, Parish Councilman Kirk Lepine said.

Isaac came up the western edge of the parish, lashing the area with powerful winds and storm surge, Lepine said.

"It came in at the worse scenario we can imagine," he said. "There's nowhere for that water to go than here."

Plaquemines Parish rescue efforts were focused Wednesday in the small enclave of Braithwaite, on the east bank of the Mississippi River. Sheriff's deputies conducted rescue missions of as many as 40 residents trapped in homes as flooding from Isaac overtook the area.

Braithwaite, just on the outside a giant floodgate that's part of the region's fortified hurricane protection system, received the brunt of Isaac's punishment when a levee failed, sending floodwaters into homes. Rescue crews in boats retrieved residents from rooftops.

Braithwaite was under a mandatory evacuation order before Isaac hit the Gulf, but some residents chose to stay. The order affected about 3,000 people, including a nursing home with 112 residents.

By noon Wednesday, Louisiana National Guard troops, sheriff's deputies and rescue crews from the Louisiana Department of Wildlife and Fisheries converged in a staging area near the gate keeping the floodwaters back. Gusty winds continued to hammer the area, hampering rescue efforts.

Just on the other side of the gate from Braithwaite and inside the hurricane protection system, David Manes, 33, rode out the storm in his house with his three sons, ages 5 to 10. Isaac's winds snapped trees in half and peeled back some of his roof's overhang, but overall the home and neighborhood fared well.

"It wasn't supposed to be this bad," Manes said. "If I had known it would've been this bad, I would've stayed with my mother in Mississippi."

During Katrina, Manes' home was ruined by nine feet of water, he said. This time around, with the nearby floodgate installed, only small puddles of rainwater pooled in his lawn.

Manes said he didn't feel lucky that his neighborhood survived Isaac generally unscathed while nearby Braithwaite was buried under a wall of water. He has friends in Braithwaite, he said. Some he's heard from, others he hasn't.

"You don't protect certain people just to save money," he said. "If you're going to do it, do it right. Build it all the way out."

State troopers escorted National Guard troops with high-water vehicles down to the area to help with rescue efforts, state police spokesman Capt. Doug Cain said. Many of the roads in the area had become impassable.

"I'm getting text messages from all over asking for help," said Joshua Brockhaus, a resident of the flooded area who helped rescue neighbors in his boat. "I'm dropping my dogs off and I'm going back out there."

Resident Alvin Sylve was preparing to evacuate. "We've never seen it this bad," he said. "The way this wind is shifting."

Flanked by marshes and water, low-lying Plaquemines Parish has been repeatedly hit by disasters - from Katrina to Gustav to the BP oil spill in 2010.

"The geography of it makes it vulnerable," Cain said. "But talk about a resilient people. They've been through this before, and they're going to make it through this one."

Isaac forced the closures of major roadways throughout the area, including U.S. 90 at the Jefferson Parish/St. Charles Parish line, the causeway over Lake Pontchartrain and LA-73 south of Plaquemines, he said.

Besides dealing with downed trees across roadways from New Orleans to Baton Rouge, state police encountered residents who may have underestimated the storm, he said. Troopers kept busy throughout the night with highway accidents, broken down cars and several DWI arrests.

The Federal Emergency Management Agency has staged supplies throughout the south in Mississippi, Alabama, Georgia, Florida, Arkansas and South Carolina. At Mississippi's Camp Shelby, the agency has 54 generators and 256,000 ready-to-eat meals. At Maxwell Air Force Base in Alabama, FEMA has 1.2 million meals, 2,134 cots and 3,800 tarps.

About 4,130 residents have sought refuge from Isaac at shelters across the state, Jindal said.

The 350 miles of levees and floodwalls surrounding and meandering through New Orleans were holding back storm surge water as designed early Wednesday, city spokesman Hayne Rainey said. The city had not received any reports of levee breaches or calls for rescues, he said.

The Lake Borgne surge barrier, a $1 billion massive structure in the eastern part of the city erected after Katrina, stopped a 15-foot storm surge from Isaac headed to the Lower 9th Ward and other parts of the city, said Bob Turner, regional director of the Southeast Louisiana Flood Protection Authority-East, a quasi-state agency created after Katrina to monitor levee improvements. Without that 26-foot-high barrier, storm water would have spilled over levees and flooded neighborhoods ravaged by floods during Katrina, he said.

"You would have had water flowing in the Lower 9th Ward again," Turner said. "The barrier did its job."

Isaac dumped about 8 inches of rain on New Orleans over the past 24 hours, seriously taxing the city's drainage pumps, which are able to pump out about 1 inch an hour, Turner said. That has led to some street flooding, but no structure flooding had been reported, he said.

Early reports from Isaac's effects were far different from the events that unfolded around Hurricane Katrina- which slammed the region seven years to the day and led to levee breaches and mass flooding of the city. The U.S. Army Corps of Engineers rebuilt the levee and floodwall system in the New Orleans area to be much stronger at a cost of $14 billion.

The storm landed at 3:15 a.m. ET just west of Port Fourchon, about 60 miles south-southwest of New Orleans, the National Hurricane Center said.

Isaac, upgraded from a tropical storm to a Category 1 hurricane midday Tuesday, first touched land in Plaquemines Parish on Tuesday evening before heading back over the Gulf of Mexico.

The hurricane center said Mississippi and southeastern Louisiana could see peak surges of 12 feet.

In New Orleans, streets were flooding, and up to 85% of residents were without power, Landrieu said.

"One of the great challenges with this storm ... is that it's going so slowly ... which means that it's going to hover over us," he told the Weather Channel on Wednesday morning. "The longer the rain and the greater the wind ... (that) continues to concern us. That wind is really, really heavy, which is why it's important you stay inside.

"We're asking people to be patient," he said.

New Orleans, devastated by Katrina, reported 60-mph winds and drenching rains. Landrieu said about 1,000 National Guard troops are positioned in the city, working with police, firefighters and standing by for rescue operations.

The historic French Quarter that forms the heart of New Orleans' tourism industry appeared to have dodged the worst of Isaac. Downed tree limbs, minor flooding at intersections and a brief electrical outage overnight were the main problems confronting the residents who stayed mostly indoors.

"Honestly, man, it's just been rain," said Huggington "Huggy" Behr, manager of Flanagan's Pub on St. Phillips, which stayed open through the night and served "about a dozen" patrons. "To us, we've seen the worst, so it's business as usual."

More than half a million Louisiana homes and businesses lost power during Isaac, and most will stay that way for at least several days, Entergy power company spokesman Chanel Lagarde said.

As of noon Wednesday, 552,000 customers were without electricity, including 85% of New Orleans, Lagarde said.

Entergy, which serves most of Louisiana, initially planned to dispatch 4,000 workers to repair the power lines once the storm passed. Since outages were so widespread, the company said it will need 10,000 workers. Crews from power companies in 24 states, through mutual aid agreements, will pitch in.

"The one thing that's really hampering us is that the winds are still here. The storm is just hanging around," Lagarde said. "Looks like it won't be until tomorrow (Thursday) that we can get out there."

Workers cannot go up in bucket trucks to do repairs until the winds drop below 30 mph.

Entergy expects it will take "several days" before the company can restore power to most of its customers. The company will not have a more accurate estimate until the storm subsides and workers can assess the damage, Lagarde said.

Lagarde said the number of outages will continue to rise as the storm travels north through the state.

Southern Mississippi was feeling the effects of the storm, but no injuries or deaths were reported overnight in the coastal counties of Hancock or Harrison, which were two of the hardest hit by Hurricane Katrina seven years ago.

Sustained winds throughout the region topped out at about 40 mph, so the main concern remains flooding from a constantly driving storm surge and what is likely to be prolonged rainfall for several days.

In Harrison County, the rising waters knocked a boat off its moorings. County Emergency Management Director Rupert Lacy said the boat slammed into Popps Ferry Bridge, forcing officials to shut it down until crews can inspect the integrity of the bridge. The bridge is one of two connecting Biloxi from the mainland, but Lacy said it could be a long time before an inspection can be done.

"We cautioned our public safety employees ... that you don't need to be out there if the winds are too high," Lacy said.

Mississippi Gov. Phil Bryant took a tour of coastal Mississippi early Wednesday and said the flooding was extensive. He told WLOX-TV that he had spoken with President Obama and requested an expedited major disaster declaration to begin the next phase of the storm response.

"Structurally, we're doing very well," said Gulf Shores spokesman Grant Brown. "A couple of homes had some vinyl siding pulled off, and a little piece of sheet metal was torn off one roof. We have some water under some lower condominium areas, but no water is in buildings, as far as we can tell."

The berm along the beach held, with one small breach. High tide in this area is expected around late morning, and officials anticipated 3- to 4-foot storm surges. That could cause some additional flooding of roads in low-lying areas, Brown said.

"All in all, we fared extremely well, with virtually no damage to speak of," he said. "We anticipate tomorrow to be a cleanup day, with business as usual Friday, Saturday and Sunday."

In Orange Beach, the storm demolished a number of boat piers and docks but caused little damage to homes, said city Administrator Ken Grimes. Some homes lost power overnight, but it had been restored this morning, he said.

The city's public beaches were open, although no swimming was allowed.

"We really did well," Mayor Tony Kennon said. "We had minimal flooding in the usual areas. We were fortunate that we were spared. Our hearts go out to the people of Mississippi and Louisiana that are having to deal with it."

Traffic and other activity was picking up. Businesses reopened under cloudy skies, off-and-on rain and occasional gusts of wind.

"By tomorrow, anyone that comes into town almost wouldn't even know something had happened here other than a major thunderstorm," Grimes said.

In New Orleans, Melba Leggett-Barnes, who stayed in her home in the Lower 9th Ward, an area leveled during Katrina, said she felt more secure than she did seven years ago.

"I have a hurricane house this time," said Barnes, who has been living in her newly rebuilt home since 2008. She and her husband, Baxter, were among the first to get a home through Brad Pitt's Make It Right program.

Her yellow house with a large porch and iron trellis was taking a beating but holding strong. "I don't have power, but I'm all right," said Barnes, 56, a cafeteria worker for the New Orleans school system.

Dean Marshall, 49, stepped into Seminole Grocery for cigarettes and beer, then returned to his apartment. Marshall said he has endured many storms and is confident flood protections installed since Katrina devastated the city would hold back the water this time. "I'm not worried at all," he said. "We're going to ride it out."

All airline flights in and out of New Orleans were canceled for a second straight day Wednesday, and the airport remained closed. Airports in other Gulf cities - including those in Pensacola, Fla., Biloxi, Miss., and Mobile, Ala. - also were closed.

Southwest Airlines planned to suspend all flights to New Orleans at least through 5 p.m. Thursday. Ordinarily, Southwest would fly about 76 flights in and out of the city on Wednesday and Thursday. Because Isaac has forced the cancellation of hundreds of flights since the weekend, most airlines have notified passengers that they can rebook their flights without having to pay a fee.

Search-and-rescue teams - including 48 boat teams deployed to areas prone to flooding and in direct path of the storm - have been mobilized, and Louisiana officials have asked teams from Texas and six other states to be on standby. Power crews, linemen and tree-trimmers are ready to restore power as quickly as possible if there are outages. Damage assessments, including aerial surveillance, could begin as early as Friday, Jindal said.

Louisiana has mobilized 40 "pods" in the southern part of the state and 20 in northern Louisiana - each designed to feed 5,000 people, Jindal said.

Across the region, schools and government offices have closed, hospitals and nursing homes have been evacuated and entire towns have been told to leave for higher ground. Tulane Medical Center in New Orleans closed outpatient services and rescheduled elective surgeries. Spokeswoman Susan Kaufmann said that after evacuating patients following Katrina and closing for several months for storm repairs, "we're highly prepared and ready to go," Kaufmann said.

The Interim Louisiana State University Public Hospital in New Orleans, which normally houses about 170 patients on-site and 29 psychiatric patients at another facility, began preparing in earnest once it was clear Isaac was going to enter the Gulf of Mexico. Tuesday morning, 500 staffers and doctors showed up, preparing for a three-day stay. Patients who were able to be discharged were sent home and off-site psychiatric patients were sent to a state facility in Pineville, La. Procedures not considered emergencies, such as elective surgeries, were canceled until Friday. The hospital is ready, partly because of lessons learned from Katrina, CEO Roxane Townsend said. "We've been hardened to be able to withstand up to a Category 4 hurricane."

Officials were concerned that residents would get complacent and decide not to evacuate or take precautions. President Obama urged Louisiana residents to follow officials' instructions regarding the approach of Isaac.

"Now is not the time to tempt fate, now is not the time to dismiss official warnings," Obama said. "You need to take this seriously."

Isaac left 24 dead in Haiti and the Dominican Republic but left little damage in the Florida Keys as it blew past. It promised a soaking but little more for Tampa, where the planned start of the Republican National Convention on Monday was pushed back because of the storm.

Isaac is the fourth hurricane of the 2012 Atlantic hurricane season, following Chris, Ernesto and Gordon. A typical season sees six hurricanes. Preseason forecasts from the National Oceanic and Atmospheric Administration called for four to eight hurricanes, while Colorado State University forecasters called for five hurricanes.

None of the other three hurricanes hit the USA, although Ernesto did make landfall in Mexico on Aug. 7.